1. Field of the Invention
The present invention relates to a control device for a hybrid vehicle and a control method therefor, and, more particularly, to a control device for regenerating the purification capacity of an exhaust gas purifying device and for charging a battery, and a control method therefor.
2. Description of the Related Art
In recent years, hybrid vehicles which have an internal combustion engine combined with an electric motor and runs on the output power from the internal combustion engine in conjunction or combination with the output power from the electric motor are in practical use. In such hybrid vehicles, the internal combustion engine is operated intermittently as needed and is selectively operable in high-efficiency operating ranges. Therefore, the hybrid vehicles have advantages in terms of fuel efficiency and exhaust gas purification performance as compared with vehicles, which run on only the output power from an internal combustion engine.
However, even the hybrid vehicles cannot run without emitting exhaust gas derived from the operation of the internal combustion engine, and require an exhaust gas purifying device for purifying the exhaust gas from the internal combustion engine.
As the exhaust gas purifying device, a storage-reduction type NOx catalyst for purifying NOx in exhaust gas from an internal combustion engine (which is hereinafter referred to also as “NOx catalyst”) and a particulate filter for purifying particulate matter in exhaust gas (which is hereinafter referred to also as “filter”) are known.
As for the NOx catalyst, a process in which the temperature of the NOx catalyst bed is increased and a reducing agent is supplied to the NOx catalyst (which is hereinafter referred to as “SOx regenerating process”) is performed to eliminate SOx poisoning, which is a phenomenon where SOx in the exhaust gas is stored in the NOx catalyst and reduces the storage capacity of the NOx catalyst.
As for the filter, when a large amount of collected particulate matter (PM) is accumulated, the filter is clogged and the back pressure in the exhaust gas is increased to the extent that the engine performance is reduced. Therefore, a process of increasing the temperature of the filter is performed by, for example, increasing the temperature of exhaust gas to be introduced into the filter to remove the collected particulate matter by oxidation (which is hereinafter referred to as “PM regenerating process”).
In the SOx regenerating process and the PM regenerating process, the engine load or the engine speed is set to a value greater than that during normal operation in order to increase the temperature of exhaust gas.
In addition, the above hybrid vehicles require a process of charging a battery for serving at least as an electric power source of the electric motor. In the battery charging process, the engine load or the engine speed is set to a value greater than that during normal operation as in the SOx regenerating process and the PM regenerating process. Therefore, every time any of the above processes is performed, the driveability and the fuel efficiency of the hybrid vehicle as a system may deteriorate.